1. Field of the Invention
The present invention relates to an image display device, and more particularly to an image display device for displaying a two-dimensional plane image (hereinafter referred to as ‘2D image’) and a three-dimensional stereoscopic image (hereinafter referred to as ‘3D image’).
2. Discussion of the Related Art
An image display device displays a 3D image using a stereoscopic technique or an autostereoscopic technique.
The stereoscopic technique, which uses a parallax image between left and right eyes of a user with a high stereoscopic effect, includes a glasses type method and a non-glasses type method. In the glasses type method, the parallax image between the left and right eyes is displayed on a direct-view display or a projector through a change in a polarization direction of the left and right parallax image or in a time-division manner. Thus, a stereoscopic image is displayed using polarization glasses or liquid crystal shutter glasses. In the non-glasses type method, an optical plate such as a parallax barrier for separating an optical axis of the parallax image between the left and right eyes is generally installed in front of or behind a display screen.
As shown in FIG. 1, the image display device using the glasses type method may include a patterned retarder 5 for converting polarization characteristics of light incident on polarization glasses 6 on a display panel 3. In the glasses type method, a left eye image (L) and a right eye image (R) are alternately displayed on the display panel 3, and the polarization characteristics of light incident on the polarization glasses 6 are converted by the patterned retarder 5. Accordingly, the glasses type method implements a 3D image by spatially dividing the left eye image (L) and the right eye image (R). In FIG. 1, a reference numeral 1 denotes a backlight unit providing light to the display panel 3, and reference numerals 2 and 4 denote polarizing plates respectively attached on upper and lower surfaces of the display panel 3 so as to select a linear polarization.
In the glasses type method, visibility of the 3D image is degraded due to crosstalk generated at the position of an upward or downward viewing angle. As a result, in the general glasses type method, the upward/downward viewing angle allowing the user to view the 3D image of good image quality is very narrow. Crosstalk is generated because the left eye image (L) passes through a right eye patterned retarder region as well as a left eye patterned retarder region and the right eye image (R) passes through the left eye patterned retarder region as well as the right eye patterned retarder region at the position of the upward/downward viewing angle. Thus, as shown in FIG. 2, Japanese Laid Open Publication No. 2002-185983 describes a method for obtaining a wider upward/downward viewing angle by forming black stripes (BS) in patterned retarder regions corresponding to black matrixes (BM) of a display panel to thereby improve the visibility of the 3D image. In FIG. 2, when observing at a predetermined distance (D), a viewing angle (α), at which the crosstalk is not theoretically generated, depends on the size of black matrixes (BM) of the display panel, the size of black stripes (BS) of the patterned retarder, and a spacer (S) between the display panel and the patterned retarder. The viewing angle (α) widens as the size of the black matrixes and the size of the black stripes increase, and as the width spacer (S) between the display panel and the patterned retarder decreases.
However, the related art image display device has the following problems.
First, the black stripes of the patterned retarder used to improve the visibility of the 3D image interact with the black matrixes of the display panel, thereby generating moiré. When a 2D image is displayed, the visibility of the 2D image is much degraded. FIG. 3 shows the results obtained by observing a 47-inch display device sample at a location 4 meters away from the display device to which the black stripes are applied. When the 2D image is displayed, moirés of 90 mm, 150 mm, and 355 mm are visible based on observation positions A, B, and C, respectively.
Second, the black stripes used to improve the visibility of the 3D image bring about a side effect allowing a luminance of the 2D image to be drastically degraded. This is because, as shown in FIG. 4(b), in the related art, predetermined portions of pixels of the display panel are covered by the black stripe patterns. Accordingly, when the 2D image is displayed, an amount of transmitted light is reduced by about 30% as compared with the case where the black strips are not formed as shown in FIG. 4(a).